ABSTRACT

This research was conducted in Ikole-Ekiti to evaluate the effects of four land use types (forest plantation, arable land, fallow land and ranchland) and soil depth on soil organic carbon fractions namely; particulate organic carbon (POC), soil microbial biomass carbon (SMBC), total organic carbon (TOC) and water soluble organic carbon (WSOC). Soil samples were taken at 0-5, 5-10, I0-20 and 20-30 cm and 0-30 cm depths at each site using soil auger. The soil samples were analyzed for physical and chemical properties. At O- 5 cm depth, fallow land had the highest TOC, (30.27 g/kg), followed by forest plantation, ranchland and arable land at 29.70, 28.57 and 19.60 g/kg respectively. At 5-10 cm, TOC significant differed across the land use, with fallow land and forest plantation given the highest values while ranchland and arable land had the least values. The SMBC at 20-30 cm depth in the fallow land was significantly different from other land use types. The arable land had the highest concentration of SMBC, POC and WSOC among the agricultural land use types but least TOC content at all depths. The carbon fractions decrease with depth across the land use type. The depth-wise distribution of soil organic carbon forms did not follow a particular trend across the land use types. Generally, soils in Ikole-Ekiti were characterized with medium to high variations in the forms of soil organic carbon except for WSOC with low variations at all depths.

Keywords: Land use, carbon fractions and depths.

TABLE OF CONTENTS
CHAPTER ONE: IMTRODUCTION    1
2.0    CHAPTER TWO: LITERATURE REVIEW    3
2.1    Soi1 Carbon    3
2.2    Soil organic carbon fractions    4
2.2.1    Total organic carbon    4
2.2.2    Soil microbial biomass carbon    4
2.2.2.1    Factors affecting microbial biomass    5
2.2.3    Water soluble organic carbon    6
2.2.4    Particulate organic carbon    6
2.3    Management practices beneficlal to SOC pool    6
2.4    Changes in Forms of Organic Carbon with Depth under the vaiious land use Managetcent
8

2.5    Land use type concept   
 
2.6    Agricultural land use types and carbon fractions    11
2.6.1    Effect of land ase on total organic carbon (TOC)    11
2.6.2    Effect of land use on particulate organic carbon (POC)    12
2.6.3    Effect of land ase on water soluble organic carbon (WSOC)    12
2.ó.4    Effect of land use on soil niicrobial biomass carbon (SMB C)    13
3.0    CHAPTER THREE: MATERIALS AND METIJOD    15
3.1    Study area    15
3.2    Site Description    15
3.3    Soi1 Sampling and Preparation    15
 
3.4    Laboratory Analysis    16
3.4.1    Routine Soil Analysis    16
3.4.2    Soil organic matter determinations    16
3.4.2.1    Determination of total organic car bon (TOC)    16
3.4.2    Determination of soil microbial biomass Carbon (SMBC)    l6
3.4.3    Determination of the particulate labile organic carbon (POC)    17
3.4.4    Determination of soil water soluble organic carbon (WSOC)    18
3.5    StatiStlcal Analysis    18
4.0    CHAPTER FOUR: RESULT AND DISCUSSION    19
4.1    Physical and Chemical Properties of the Study Site    19
4.2    Effect of Land Use on Total Or ganic Carbon    22
4.3    Effect of Land Use on Particulate Organic Carbon    24
4.4    Effect of Land Use on Soil Mlcrobial Biomass Carbon    24
4.5    Effect of Land Use on Water Soluble Organic Carbon    25
4.6    Relationships between orgame carbon fractions and selected soil pioperties in    fallow land
    26
4.7    Relationships between organic carbon fractions and selected soil properties in arable land

4.8    29
Relationships between organic carbon fractions and selected soil properties in forest

plantation land    29
4.9    Relationships between organic car bon fractions and selected soil properties in ranch land
29
5.0    CHAPTER FIVE: SUMMARY AND CONCLUS ION
REFERENCES    35
 
LIST OF TABLES
TABLE    TITLE    PAGE
1    Physical and Chemical Properties of the Land Use Types    20
2    Effect of Different Agricultural Land Use Types on various forums of Soil Organic Carbon Fractions in Ikole-Ekiti    23
3    Means, Range, Standard Deviation and Co-efficient of Variation of forms of Soif Organic Carbon in Agricultural soils in Ikole-Ekiti    27
4a    Correlation table of Soit Organic Fractions with soil physico-chemical properties for fallow land    28
4b    Correlation table of Soi1 Organic Fractions with soil physico-chemical properties for Arabie Land    30
4c    Correlation table of Soil Organic Fractions with soit physico-chemical propertles for Forest Plantation    31
4d    Conelation table of Soit Organic Fractions with soil physico-cheinical properties for Rancliland    32

CHAPTER ONE
1.0    INTRODUCTION
Soils store two or three times more carbon titan that wrnch exists in the atmosphère as CO2and 2.5-3 times as much as that stored in plants in the terresti ial ecosystem (Post el al, 2000; Houghton and Skole, 1990). Schirnel el al. (2000) pointed out that the knowledge of the spatial distribution of soil organic carbon is an important requirement for understanding the relief of soils in the global carbon system.
Soil quality is the capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality and proinote plant and animal health and thus has a profound effect on the health and productivity of a given ecosystem and the environment related to it. The type of land use system is an important factor controlling soil organic carbon levels since it influences the amount and quality of litter input, the litter decomposition rates and the processes of organic matter stabilisation in soils (Römkens et u/., 1999; Eaton et al., 2007). The total organic carbon (TOC), soil water soluble carbon (WSOC), soil lnicrobial biomass carbon (SMBC) and particulate or labile organic carbon (POC) are some of the soil pi'operties that are used as basic indicators in assessing soil quality. The soil miciobial biomass (SMB) is a srnall but key component of the active soil organic matter (SOM) povl and serves as a source and sink of soil nutrients. lt has been used to understand soil nutrient dynaniics and as an ecological marker. The reduction of SOC will lead to a decrease in soil fertility, soil nutrient supply, porosity and an inciease in soil erosion (Gray and Morant, 2003).The POC consiste of partly decomposed plant and animal iesidues with a rapid tumover, it is more iesponsive to management factors and it is believed to make a greater contribution to nutrient cycling (Janzen et al., 1992). WSOC is considered as a most mobile and reactive soil carboH source which modulates a number of physical, chemical and biological processes in both aquatic and terrestrial environments (Sclinabel el al., 2002; Marschner and Kalbitz, 2003; Havorson and Gonzalez, 2008). In most soils, the inajority of organi' carbon is in insoluble form except for a srnall fraction that is water soluble and not yet leached out. This fraction of organic carbon is called the water soluble organic carbon (WSOC).
The public concern about the issue of global climate change has emphasized the need for developing and implementing strategies of agro-ecosystem management that will reduce carbon dioxide concentration in the atmosphere as well as improving soil fertility, SOC storage and the
 
dynamics of C shock are important in evaluating the impact of agro ecosystem management on global climate change. Soils i'epresent an important t•-rrestrial stock of C.(Smith e/ o/.,2008). Thus, the dynamics of SOC as affected by agro ecosystem to a large extent affects the carbon dioxide concentration in the atmosphere as well as even the global climate change (Tan and Lal, 2005). Recent interest in evaluating soil quality has been stimulated by the increasing awareness that the soil is a critiCally important component of the earth biosphere that functions not only in the production of food and fiber but also in the maintenance of environmental quality as related to agro ecosystem management and in formulating and evaluating sustainable agricultural and land use policies (Huang, e/ a/„ 2007). in Nigeria, studies have been conducted on the use of SOC, and SMBC to evaluate the effects of managemen practices such as legume rotation on soil fertility (Granatstein and Bezdicek, 1992; Adebayo et al., 2006), but there is dearth of information on the assessment of soil quality under different agro ecosystems using the TOC, POC, WSOC and SMBC (Yusuf e/ al., 2009). This study was carried out to assess the quality and quantity of various forms of soil organic carbon under forest plantation(oil palm, cashew and teak), arable land cultivation(cassava, yarn, vegetable and maize), ranchland and fallow land. This will provide Information on the characterization of SOC and qualitative data on dynamics and nutrient cycling across major land uses.
The general objective was to determine the variability of soil carbon across different agricultural land use in Ikole-Ekiti. The specific objectives were of the study were to;
Evaluate the dynamlcs Of SOC under different agricultural landuse.
Investigate the relationship between forms of organic carbon and some selected soil properties.